The combined heating effect of human-emitted greenhouse gases increased 1.5 percent between 2012 and 2013, according to an index maintained by scientists at the National Oceanic and Atmospheric Administration in Boulder.

The 1.5 percent increase, announced Friday, brings the total increase in such gases added to the atmosphere to 34 percent since 1990.

The data is tracked through NOAA's Annual Greenhouse Gas Index, maintained by the Global Monitoring Division of the Boulder-based Earth System Research Laboratory at NOAA.

The latest data on the AGGI was released Friday by Jim Butler, director of the Global Monitoring Division, in Vienna where he is participating at the annual meeting of the European Geosciences Union.

"The significance is that it's an annual reminder that the warming influence of greenhouse gases in the atmosphere continues to rise as we continue to emit greenhouse gases, and it can take a long time to recover from what we're seeing, should we choose to go that direction," Butler said in a phone interview.

Reversing the continuing trend — the last decade has seen steady increases of 1.4 to 1.5 percent — won't be easy. The Kyoto Protocol, which the United States has declined to ratify, set as a goal reducing greenhouse gas emissions to 1990 levels.

The latest data shows the trends continuing to move in the other direction, which Butler said will continue to turn up the dial on Earth's "electric blanket."

"It will take a while to get back already," Butler said, "simply because some of these gases are very long-lived. The chlorofluorocarbons are already declining, but one of them has a lifetime of 120 years and the other is around 50 years.

"And much of the carbon dioxide that has already been emitted is going to remain in the atmosphere for a very, very long time."

Carbon dioxide is the largest greenhouse gas contributing factor to climate change, calculated to be responsible for 87 percent of the past year's increase.

Researchers from the Cooperative Institute for Research in Environmental Sciences at the University of Colorado team with NOAA scientists to produce the index and assist in sampling air and data analysis. The index provides scientists and policy-makers information used for developing a better understanding of climate change in the present day, as well as its possible future impacts on society.

'We actually know what to do'

Friday's updating of the greenhouse gas index comes little more than a month after a report, also from NOAA's Global Monitoring Division, that carbon dioxide levels at its Mauna Loa Observatory in Hawaii — considered a global benchmark monitoring site — had reached 400 parts per million in mid-March, two months earlier than it had done so in 2013.

They continued to top the 400 ppm mark through much of April and are forecast to continue at historically high levels into early June, at which point they should diminish as vegetation in the Northern Hemisphere begins to absorb carbon dioxide during the growing season.

"These increases that we're seeing are close to 100 percent manmade," said Pieter Tans, a senior scientist in NOAA's Global Monitoring Division.

"We actually know what to do, broadly, but we're not doing anything much," Tans said, noting that carbon dioxide already in the oceans and Earth's atmosphere will not disappear "for thousands of years."

"If we want to avoid catastrophic climate change, it is imperative that we bring these emissions to zero — not immediately, but we must get there. We need to cut emissions in half in a decade or two, and then we need to keep at that until we bring them down to zero."

Tans said the "good news" is that other countries, such as Sweden and Germany, are already showing that emissions can be cut through steps such as using high-efficiency light bulbs and construction of energy-efficient buildings that require less heating in winter and less cooling in summer.

"The beauty is that if you do this kind of thing, it creates jobs," Tans said. "Isn't that what you want? It's a jobs program with a very beneficial long-term outcome. It's a positive investment in our long-term future."

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